The objectives are: 1) to establish the role of complement in the pathogenesis of disseminated intravascular coagulation (DIC), 2) to delineate mechanisms which operate in the interaction of complement with the hemostatic system, and 3) to define possible alterations of the complement system in patients undergoing DIC. The components of the complement system will be measured in the serum of rabbits infused with thromboplastin, as well as in serum of patients with DIC syndromes. The mode of interaction of thromboplastin with the complement system will be explored in vitro with preparations of highly purified thromboplastin and complement components. The role of C3 in DIC produced in rabbits and mice by thromboplastin infusion will be studied; C3 will be inactivated by injection of an anti- complement factor obtained from cobra venom.